When I was on the spanners I used to do high power engine runs.
Now I'm a pilot and I don't.
My personal opinion is that the Engineers are probably as safe if not safer than the pilots for this particular job purely because of recieving training in this particular job.
Every now and then we get a c0ck up with an airborne situation, every now and then we get a c0ck up with a ground based situation. Such is Human failability. The only panacea is to be conservative in how you operate, be it on the ground or in the air.